For certain applications of hot melt adhesives and sealants, the adhesive/sealant is transported and supplied in bulk form, typically in small slats, pellets, blocks, pillows, or chips. These products are solid at room temperature, and therefore, need to be heated to a liquid state for application. The product is inserted in a melt tank, heated to a liquid or flowable semi-liquid state, and then pumped through a heated hose to a heated manual or automatic gun for application. This type of hot melt dispensing system is commonly used in packaging (cereal boxes), automotive applications (headliners), and various other industrial applications.
The tank for melting the adhesive/sealant is typically a single composite unit with attached components such as heating elements, sensors and pumping units. The melt tank is a cast or extruded aluminum box or cylinder with an opening at the top sufficient to accept quantities of the bulk adhesive. The melt tank capacity is routinely measured in pounds and can vary in maximum capacity from seven pounds to 100 pounds. However, some melt tanks can be smaller or larger in capacity.
The solid bottom of the typical melt tank is drilled and reamed to accept cartridge style heating elements or has cast-in heating elements. These heating elements are needed to sufficiently heat the bottom and sides of the tank to transfer the necessary heat through the metal to melt the adhesive/sealant to the desired liquid or flowable state. The heat created at the bottom and sides of the melt tank must also transfer into the pumping mechanism to maintain the flowable state of the adhesive/sealant. Therefore, either at the bottom or through the opening at the top of the typical melt tank, the pumping mechanism is attached to the melt tank in such a way that it comes in direct contact with the heated bottom of the melt tank. With its integral pump and heating components, the melt tank is typically bolted to and supported by a metal frame or base assembly to which all other system components are secured such as electronic temperature and process controls. This assembly of the typical melt tank makes removing the melt tank difficult, particularly for cleaning.
Repeated use of the melt tank causes a residue of char and degraded adhesive resins to build up primarily along the inside wall and bottom of the melt tank. This build up eventually finds its way through the pump, hoses and application guns to affect the overall performance of the equipment and the purity of the adhesive/sealants. The problems encountered include gummed up filters, premature pump wear, clogged hoses and dripping gun nozzles. Even used on a regular basis, commercially available tank purge and flushing materials do not clean the melt tank sufficiently. Char and burnt resins continue to build up. The best way to clean the melt tank is to remove it from the system and have it baked or chemically stripped and cleaned, and finally re-installed. Accordingly, removal of the melt tank from the rest of the assembly is essential to thoroughly clean the melt tank thereby maintaining a high quality product.
However, in existing systems, the melt tank side walls are welded to the surface of a heating plate. Inserted in the heating plate is the previously mentioned cartridge style heating elements. Bolted and attached to the bottom of the heating plate is a complete pump assembly with a flow control device. The melt tank with attached heating plate is bolted to the steel base assembly using hardened steel bolts and heat insulating washers. Removing the melt tank for cleaning or replacement requires the removal of the heating elements, temperature sensing device, pump assembly with the flow control device, and removal of the steel bolts and heat insulating washers. This process requires significant time and effort resulting in significant down time for the equipment.
Even after the melt tank is removed from the steel base assembly, access to the interior of the tank is cumbersome making cleaning still difficult because the heating plate is welded to the tank. Additionally, replacement of the melt tank requires replacing the bottom heating plate or else significant labor would be required to unweld, and reweld, the tank side walls where they are joined to the heating plate.
Wherefore, it is an object of the present invention to provide a design for a melt tank which may be removed from the rest of the hot melt assembly prior to melt tank repair, cleaning and/or replacement without removing any other attached components.
Another object of the present invention is to provide a design of the melt tank which does not require replacement of the heating plate during melt tank repair, cleaning and/or replacement.
Still another object of the present invention is to provide melt tank design that does not require the unwelding, and rewelding, of the tank side walls to the heating plate during melt tank repair, cleaning and/or replacement.